Spatial displays viewed without user worn apparatus, such as autostereoscopic displays, integral imaging displays, volumetric displays, holographic displays, aerial-image displays, and infinity displays present images which appear to have various spatial qualities. These and other various spatial display technologies have widely varying spatial qualities, imaging methods, limitations, physical construction and spatial image presenting capabilities. Autostereoscopic displays, such as the parallax barrier or lenticular methods, provide a multitude of viewing zones at different angles with the image in each zone appropriate to that point of view. Typically, a fine vertical grating or lenticular lens array is placed in front of a two-dimensional (2D) display screen. A stereoscopic image is divided into two alternating vertical bands, comprising alternating left/right views, and displayed on the 2D display screen. If the observer's eyes remain fixed at a particular location in space, then one eye can see only the right view bands through the grating or lens array, and the other eye can see only the left view bands. The eyes of the user must be within separate but adjacent viewing zones to see a stereoscopic image, and the viewing zone must be very narrow to prevent image distortions as the observer moves relative to the display. These techniques have several drawbacks.
Autostereoscopic displays typically require a large display resolution. Each eye sees only half the horizontal screen resolution, therefore the image's resolution is significantly reduced. If the displays provide multiple views of a stereoscopic image, each view provided lowers the display's resolution in half. Also, the observer must remain within viewing zones. Additionally, as the observer focuses on a single plane, conflicts between convergence and accommodation rapidly lead to eyestrain. The observer cannot focus on images of varying depth, as with other three-dimensional spatial displays, such as volumetric or holographic displays.
Projection devices are known in the art that project images so that they appear to float in the air. Most prior art aerial projection systems typically use a three-dimensional (3D) physical object as the source of the image. However, this cannot produce an arbitrary or moving image. Some methods produce floating images by either reflecting an electronic display from one or more curved mirrors, viewing an electronic display through an optical system comprised of retroreflectors combined with beam splitters or viewing an electronic display placed behind one or more lenses. These methodologies are termed reflective real-image displays or transmissive real-image displays, respectively. The imagery produced by a typical real-image display, is typically planar. The imagery has some spatial qualities, but the image otherwise has no true 3D spatial qualities.
Some methods create transmissive floating planar imagery from an electronic display placed behind a first Fresnel lens located behind a second Fresnel lens, which focus the light from the image source in front of the second Fresnel lens. They may also combine two floating planar images by aligning two image sources with two pairs of Fresnel lens (4 lenses in total), and optically combining them with a single half-silvered mirror (beam splitter). Two planar images are viewed by an observer, both floating in space, one in front of the other, comprised of 2D foreground and background imagery. Some of these methods suffer from the fact that both floating planar images appears to float within the housing, rather than preferably extending beyond the housing for increased viewability and impression of spaciousness. Additionally, the imagery produced by the two full set of optics and displays, has limited spatial impression as the imagery is merely comprised of two overlapping planar images separated by a small amount of space. More specifically, the imagery is lacking true three-dimensionality, as it has no smooth or deep spatial visual qualities.